Excellent, this confirms what I thought happened.
- You upgraded DSM 7.
- During that upgrade, DSM Package Center gave you PMS 1.21.0.3744 (the BETA) package
- 1.21.0 isn’t compatible.
- Installing 1.27.2 manually, did an invisible “Upgrade” (which it’s supposed to) and moved the BETA data to PlexMediaServer.
- Since you didn’t have time to Manual Install, DSM itself broke you ownership.
To fix this.
- I have a How-To,
- It tells you about all the changes to Plex for DSM 7
- It then tells you the Step-by-Step (Don’t skip or miss any) process to migrate all your DSM 6 server data to DSM 7.
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Depending on how many files you have indexed, this can take anywhere from minutes, to hours, to days. Estimated speed is 3 minutes for each 1000 files you have indexed in PMS.
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You cannot interrupt the install. DO NOT refresh the “Installing” page -OR- Restart the NAS.
– DSM may issue a false warning (if you miss a step) – which you can ignore -
The installer is intelligent now, It will give you step-by-step instructions of everything you need to do.
My How-To is the supplement to it WITH SCREENSHOTS 
TO GET YOU STARTED
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Uninstall the DSM 7 package - use the ERASE option.
– This removes the unusable/empty DSM 7 server in “PlexMediaServer” -
Install the DSM7 package again.
– It will start running its checks
– If it doesn’t like anything, it will stop with the instructions printed in the popup page. Follow those instructions. They are custom to your machine.
Please read the above link
Here is the HOW-TO perform the migration, step by step.
If questions, ASK. It’s easier to get it right than it is to clean up afterwards
